1. Field of the Invention
The present invention relates to self-luminous elements including a fluorescent substance layer having fluorescent substances in a hermetic enclosure, where a fluorescent substance light-emits due to electron beam excitation. Particularly, the present invention relates to self-luminous elements, each having a new gas occlusion material for occluding unnecessary gases, which is disposed in an envelope to make and maintain a high degree of vacuum degree inside the enclosure.
2. Description of the Prior Art
In self-luminous elements, an envelope is hermetically sealed to maintain the inside thereof in a hermetic state. Such a closed space is maintained to a high degree of vacuum, such as less than 1×10−3 Pa. To realize such a state, high-melting point metal materials, such as Ti, Mo, Ba, Zr, and the equivalents, each which has the function of absorbing residual gases and removing them from the gas phase, have been used as getter materials (hereinafter, referred to as getter).
A fluorescent display tube, shown in FIG. 14, is a type of self-luminous element that light-emits an electron beam excitation luminous material such as a fluorescent substance. The fluorescent display tube includes an electron source 600 disposed in a vacuum hermetic envelope, and an anode having a fluorescent substance layer 400 on which a fluorescent substance, which glows due to impingement of electrons irradiated from the electron source, is coated. It is required to maintain the inside of the vacuum hermetic envelope in a hermetic state and to maintain the inner surface of the vacuum envelope and the surface of the fluorescent substance in a clean state.
In conventional self-luminous elements employing the electron beam excitation emission, an expensive getter ring 110, which has a metal container filled with a getter material such as Ba—Al alloy, is used to maintain the inner surface of the vacuum hermetic envelope in a high degree of vacuum and to maintain the inner surface of the envelope and the surface of the fluorescent substance in a clean state.
In plasma display devices being self-luminous elements, unnecessary gases, other than the display gas such as a plasma excitation gas, that form within or enter the envelope after it has been evacuated to a high degree of vacuum, adversely affect the operational life of the device. Therefore, it is required to remove unnecessary gases inside the plasma display device.
In order to maintain the luminous characteristics of an EL display device being a self-luminous element, after the luminous elements have been sealed inside the envelope, the inside thereof must be maintained to minimize the formation or introduction of unnecessary gases. FIG. 14 depicts a getter for fluorescent display tube being one of electron beam excitation luminous elements. An expensive getter ring 110, which has a metal container filled with a getter material such as Ba—Al alloy, is heated with high-frequency induction to form an evaporation film.
As to the getters for fluorescent display tubes, various techniques have been developed to prevent harmful effects due to the high-frequency induction heating. For example, as shown in FIG. 14, the magnetic core 802 is placed around the high-frequency induction heating core 803 to prevent the spreading of magnetic field. (For example, refer to Japanese Patent Laid-open Publication No. Tokkai-hei 7-282728 and Japanese Patent Laid-open Publication No. Tokkai 2001-76653) However, the problem is that the above-mentioned getter ring is expensive and requires a space for installation in the vacuum envelope and requires labor for mounting a getter ring.
A technique has been disclosed for preventing the problem of forming an evaporation film through the r-f induction heating of the getter ring and of effectively using the man-power and the space (for example, refer to Patent Publication No. WO00/54307). In this technique, a non-evaporation type getter (NEG) formed of metals of one or more types or an alloy of them, on the upper surface of an insulating substrate constituting a display element is fabricated through a printing method or sputtering method. The metals are selected from the group consisting of Ti, Cr, Al, V, Nb, Ta, W, Mo, Th, Ni, Fe, and Mn. The non-evaporation type getter (NEG), however, is expensive and requires the activation workability.
Moreover, there is a technique for preventing the trouble occurring when an evaporation film is formed by h-f heating a getter ring being a getter material for a fluorescent display tube and effectively using the man-power and the space. In this technique, a Ba—Al alloy or Mg—Al alloy, which does not contain an additive metal such as Ni, is press molded in a disk, oval, or rectangular shaped getter. Then, the getter is mounted in the electron tube such as a fluorescent display tube, using metal wires or fritted glass. The technique of flushing the getter through the laser beam heating and thus forming a getter mirror film has been disclosed (for example, refer to Japanese Patent Laid-open Publication No. Tokkai-hei No. 2002-343233).
In addition to the technique of using a metal having the getter effect and maintaining a clean atmosphere in the vacuum envelope, the technique of using TiO2 or ZnO2 as an auxiliary getter material is disclosed as described below. TiO2 and ZnO2 are used as a getter material. However, if a material absorbs O or H, other chemicals may be mixed in a getter material. Such materials are dissolved in a fixing solution to make a solution, and then the solution is coated on support members. The concentration of the getter material in the coating solution is set to 2 to 5 wt %. However, the fixing solution evaporates during the sealing step and is drawn out. Finally, the titanium oxide remains as a getter material.
In order to effectively derive the absorption effect of the getter mixed in the fixing material 10, it is effective to bake the substrate above at least 400° C. That is, the technique is disclosed of improves the getter effect by deoxidizing TiO2 into TiO or Ti through the baking step (refer to Japanese Patent Laid-open Publication No. Tokkai No. 2000-340140). However, this technique has a problem in a practical use because only an auxiliary effect of creating and maintaining a high degree of vacuum degree was confirmed.
In order to maintain a high degree of vacuum such as 1×10−3 Pa in the closed space, such as the vacuum display device of the present invention, materials, having the function of absorbing residual gas molecules and removing them from the gas phase, for example, high melting point metal materials, such as Ti, Mo, Ba, and Zr, have been employed as getter materials. The Ba series getters have been practically used as getters generally usable in a temperature range of 140° C. to 120° C. However, a high melting point metal material, such as Ti, Mo, or Zr, has not been used practically as a getter material. Powders of high melting point metal, being the getter material, may generally be unstable because it can catch fire when in contact with the air. Moreover, the metal powders do not often have a sufficient gas occlusion capability.
Various techniques have been developed to obtain getter materials, which are safe and easy to handle, and to improve the occlusion efficiency of residual gases of a getter material. The problem, however, is that any one of those techniques requires a room for disposing a getter material and requires the step of activating the surface of the metal getter material though h-f induction heating or resistance heating after the getter material has been placed in the envelope.